1. Field of the Invention
This invention relates to methods for deforming a workpiece and, more particularly, to methods for the continuous extrusion of an elongated workpiece, such as a rod, of indefinite length to form an elongated product, such as a wire, of indefinite length.
2. Description of the Prior Art
In the art of deforming elongated workpieces of indefinite length, so as to form elongated products of indefinite length, continuous hydraulic extrusion techniques are known. For example, my U.S. Pat. No. 3,740,985, an application for the reissue of which has been filed on Jan. 4, 1974 under Ser. No. 430,984, and my copending application, Ser. No. 612,875, filed Sept. 12, 1975, disclose two embodiments of apparatus, and related methods, for the continuous hydrostatic extrusion of elongated products of indefinite length. These embodiments incorporate moving trains of gripping element sectors for applying forces to workpieces of indefinite length through suitable shear-transmitting media. In each of these embodiments, a workpiece is advanced linearly, due to the action of shear forces transmitted by the medium utilized, while being subjected to a pressure gradient increasing in the direction of the linear advance. Once the pressure level has become sufficient to increase workpiece ductility substantially, the workpiece is forced through a die which deforms the workpiece into an elongated product.
It is also known to extrude an elongated product of indefinite length by advancing an elongated workpiece of indefinite length along a curved path toward and through a die, utilizing a single rotary member having a grooved, radially outermost surface. The workpiece is held in the groove of the rotary member by a stationary member located radially outwardly from the rotary member. The contact area between the workpiece and the groove in the rotary member is greater than that between the workpiece and the stationary member, so that an imbalance of friction forces causes the workpiece to advance with the rotary member. Such techniques are disclosed in U.S. Pat. No. 3,765,216 and U.S. Pat. No. 3,872,703, both issued to D. Green, and in ASME paper No. 73-WA/PT-2, by C. Etherington, entitled, "Conform -- A New Concept for the Continuous Extrusion Forming of Metals".
With particular reference to the extrusion technique disclosed in the two Green patents and the ASME paper, the use of a stationary member to engage a workpiece and maintain the workpiece within a groove in a rotary member necessarily imposes upon the workpiece a frictional resistance, due to the contact with the surface of the stationary member, which opposes the advance of the workpiece toward the die. This is clearly a source of inefficiency in the extrusion process. Moreover, such process does not readily permit the provision of efficient mechanisms for supporting a continuously increasing compressive pressure to which the advancing workpiece is subjected during hydrostatic extrusion of the workpiece.
A technique which seeks to overcome the frictional resistance problem associated with the extrusion process taught in the Green patents and the ASME paper is disclosed in U.S. Pat. No. 3,911,705 to W. G. Voorhees. The Voorhees approach utilizes a flexible band between the stationary member and the workpiece, the band being permitted to advance with the rotary member and the workpiece, and having a lubricant on the surface of the band which contacts the stationary member in order to minimize the frictional drag on the workpiece. However, no mechanism is available in such an arrangement for providing an effective seal about the edges of the band so as to prevent entry of lubricant into the groove in the rotary member, such as might cause contamination and/or rod slippage, and so as also to prevent flash metal extrusion about the periphery of the band at high pressures. Moreover, the use of a relatively thin, flexible band maintained in tension limits the maximum extrusion pressure which the apparatus can support.
Two further processes, which are of some interest in connection with the continuous deformation of an elongated workpiece of indefinite length, so as to form an elongated product of indefinite length, are disclosed in U.S. Pat. No. 3,922,898 to W. G. Voorhees, and in an article by Betzalel Avitzur entitled, "Extrolling: Combining Extrusion and Rolling", in the July 1975 issue of Wire Journal at page 73. Each of these publications discloses the provision of two circular blocks or rolls, which are mounted on parallel axes such that their radially outermost surfaces cooperate to define a region therebetween for gripping an elongated workpiece. Simultaneous rotation of the two circular blocks or rolls causes an elongated workpiece extending tangentially into such region to advance tangentially therewith, so as to be extruded through a suitably positioned die which projects into the path of the advancing workpiece. In addition, the Avitzur article describes a rolling operation taking place as the workpiece is advanced between the rolls and into the die, such article also describing the presence of a protrusion on the radially outermost surface of one of the rolls, mated with a groove on the radially outermost surface of the other roll to form the workpiece gripping region. Clearly, the length of contact between the workpiece and the circular blocks or rolls is relatively limited in systems of this general type, and consequently, the maximum extrusion pressure which can be imparted to the advancing workpiece is similarly limited.
Clearly, it would be quite advantageous to provide improved methods for deforming an elongated workpiece of indefinite length so as to produce an elongated product of indefinite length, which improved methods avoid the previously mentioned shortcomings of certain of these techniques.